The noise from an electric motor comprises mechanical noise and electromagnetic noise. Factors resulting in mechanical noise include the way the motor end cap is assembled to the motor housing, the sliding contact between brushes and commutator, rotor coaxiality etc. Factors resulting in electromagnetic noise include stator poles, rotor core, rotor winding slots, etc.
One existing motor in HVAC applications is a DC motor having two stator poles and twelve rotor winding slots. The motor comprises two diametrically opposite brushes. Harmonic noise is emitted when the motor is running, such as 12th harmonic, 24th harmonic, 36th harmonic, 48th harmonic, etc. This harmonic noise is felt to be unpleasant by some people, especially with long term exposure as occurs in HVAC applications.
Therefore, there is a desire for a lower noise motor in HVAC application. There is an additional desire for a motor with low noise and an improved electromagnetic compatibility (EMC).